Osteo-arthritis is the chronic degenerative disease associated with joint pain and loss of joint function. It is caused by 'wear and tear' on a joint. Knee is the most commonly Involved joint. Disease is so crippling that patient is unable to walk independently from bed to bathroom. The major causes of osteo-arthritis are age, gender, obesity, medical condition and hereditary. The signs and symptoms of osteo-arthritis are pain, joint stiffness, joint swelling, and loss of function. No blood tests are helpful in diagnosing osteo-arthritis. Management of osteo-arthritis includes non-pharmacological, pharmacological and surgical. A relatively new procedure is viscosupplementation, in which a preparation of hyaluronic acid is injected into the knee joint. Hyaluronic acid is a naturally occurring substance found in the synovial fluid. It acts as a lubricant to enable bones to move smoothly over each other and a shock absorber for joint loads. The decrease in the elastic and viscous properties of synovial fluid in osteo-arthritis results from both a reduced molecular size and a reduced concentration of hyaluronic acid in the synovial fluid. Viscosupplementation may be a therapeutic option for individuals with osteo-arthritis of the knee. Viscosupplementation has been shown to relieve pain in many patients who cannot get relief from non-medicinal measures or analgesic drugs. This article is to know the mechanism of action, patients' selection criteria, rationale and efficacy of viscosupplimentation in the management of osteo-arthritis of knee.